Exterior surface of a boat hull



FIG. 1 is a rear perspective view of the exterior surface of a boat hull showing my new design;

FIG. 2 is a front perspective view thereof;

FIG. 3 is a side elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a front elevational view thereof; and

FIG. 6 is a bottom plan view thereof. 

The ornamental design for the exterior surface of a boat hull, as shown and described. 